Magnetic sound reproducer having two styli



MarCh 20, 1951 N. c. PICKERING 1 2,545,859

MAGNETIC SOUND REPRODUCER HAVING TWO STYLI Filed Jan. 3l, 1949 Illli MHH/"UWM,., Win

IN1/@MORI /Vamzau K Hr/erngj HTTOWEYS Patented Mar. 20, 1951 MAGNETIC SOUND REPRODUCER HAVING TWO STYLI Norman C. Pickering, Rockville Centre, N. Y., as-

. signor to Pickering Associates, Inc., Oceanside,

N. Y., a corporation of New York Application January 31, 1949, Serial No. 73,810

3 Claims.

This invention relates to an improved magnetic sound reproducer and has particular vrelation to a multi-stylus sound reproducer of the type having a plurality of styluses facing in different directions so that diierent sides of recordings may be readily played, particularly where automatic record changers or selectors are employed.

Attempts have heretofore been made to provide sound reproducers having a pair of styluses facing in opposite directions by mounting two complete sound reproducers back to back. These have not been altogether satisfactory due to various reasons, for instance, the lack of uniformity between the two reproducers, the excess weight and added expense and the necessity of switching the power from one unit to the other unit since they cannot be connected in parallel. Attempts have also been made to provide a doubleended stylus mounted at a center point. However, these likewise have not been satisfactory Since the upper end of the stylus forms an overhanging part which is free to vibrate at some natural period in a simple reed motion and this results in a tendency to produce a whistling sound, distortion and increased noise at the resonant point. It also results in undue accentuation of frequencies at orv near the point of resonance and increases the record wear at these points.

It is an object of the present invention to overcome these diculties and disadvantages and to provide an improved multi-stylus sound reproducer having a pair of styluses facing in opposite directions which operate with a high degree of uniformity and which will accurately reproduce the sound recorded on a record with a minimum of distortion and wear on the record.

f In the accompanying drawing- Fig. l is a side view with portions of the cas- .ing removed and', in section, of a sound reprololucer embodying my invention;

Fig. 2 is a longitudinal sectiona1 View of the reproducer;

Fig. 3 is a sectional View at right angles to Fig. 2 on the line 3 3 of Fig. 2;

Fig. 4 is a sectional view on the line 4--4 of Fig. 3;

Fig. 5 is a detailed sectionalview showing one of the armatures and its. relationship to the coil of Fig. 3;

(0 1. irs-100.41)

The reproducer is shown as mounted upon the end of one conventional type of tone arm I3. Thus, a block of insulating material I5 is attached tothe tone arm by means of screws I4.

A pair of metal plates I6 made of magnetic material such ias iron, nickel or an alloy thereof are mounted in grooves on the two sides of the insulating block I5, as appears in Figs. l and 2, and project outwardly from the end thereof. The plates I6 serve as a part of the supporting structure and also form part of the magnetic circuit. To help retain the structure in assembled relationship a pair of cross-braces I1 made of non-magnetic material such as copper, brass or the like are'connected between the two plates in spaced relationship. The cross-braces may be connectedv to the plates in any desired manner as by being provided with lugs I8 `extending through apertures in the plates and being upset or riveted therein.

' yThe magnetic force is provided by a pair of permanent bar magnets I9, likewise extending between the plates and having a tight frictional t with the plates. The poles of the magnets face in the same direction so that they are connected in parallel relationship.

As previously stated, my present reproducer is `a multi-stylus unit and with this in mind I provide a separate magnetic gap for each of the stylus supporting armatures. Thus, it will be seen that the plates I6 are each provided with a pair of double pronged pole pieces 20 preferably formed integral with the plate and extending inwardly from the upper and lower edges thereof intermediate the cross-braces I'I. The pole pieces 20 of the two plates are disposed in the same plane and extend towards each other with the bifurcated ends in confronting relationship thereby creating a pair of gaps 2l and 22 in the magnetic circuit.

Associated with the fixed system of the sound reproducer is a current generating system in the form ofV a coil I2 of elongated form with the two ends thereof being of balanced or similar structure. The coil is positioned between the plates I6 and is embraced by the pole pieces 2Q with the central elongated opening of the coil in alignment with the two gaps. It should be noted that the two gaps aredisposed in aligndesigned for use with lateral cut records but it should be understood that my invention is equally applicable to Vertical cut records. Each of the moving systems-consistsoi a cantilever spring 23 mounted at one end on one of the cross-braces l1 and extending outwardly to a point in align.m ment with the gap between the pole pieces adjacent the cross-braces. Itwilll beffse'en that the cantilever spring 23 of the moving system lli.' is mounted on the central portion. of the. outer cross-brace I7 on one side of` the unit and the cantilever spring of the other moving systemV Il is mounted on the inner cross-brace on the opposite side of the sound reproducer.

Mounted adjacent the free end of each.v of the cantilever springs is a tubular armature 24 made of a magnetic material, preferably an alloy of nickel* and iron in which the nickelY content ranges between 40% and 60% by weight; The

armature should be mounted adjacent its upper end so as toY eliminate overhanging parts with their accompanying disadvantages.

The armatures of the two moving systems eX- tend through their respective gaps in opposite directions as shown most clearly in Fig; 3 and each is centrally positioned between the pole pieces and between the two sides of the coil. In` this connection, the two armatures should be disposed in the same proximate relationship to the coil |but adjacent opposite ends thereof.

The lower end of the armature supports a stylus in a suitablemanner. In the accompanying drawing'I have shown the lower end of each armature' as being provided with a lter system in the form oi" an integrally formed spring 25. In this connection the main tubular body of the armature 24 is made of the magnetic alloy, in its soft condition. The spring portion 25' is disposed at an angle to the body portion as shown and has been work-hardened so as to impart satisfactory' spring characteristics thereto. This can be accomplished in the manner taught in my above referred to copending patent application by striking the filter portion ofthe armature a blow of suicient force to Hatten the tube and bring the two walls thereof together and to work-harden the material therein. The spring portion 25 is formed with an aperture near its outer end as shown which is iitted with an'eyelet 26 in which a jewel stylus 21 is mounted in a well-known manner. rlhe purpose of the spring lter 25 is to provide additional compliance in a vertical direction so as to filter out undesirable high frequencies resulting from imperfections in the' shellac surface of the record.

In order to provide additional resistance to displacement in a longitudinal direction a tie-wire or cord' 28 may be connected between each cross brace IT and the adjacent armature at a point spaced a short distance from the free endthereof. It will be seen that. due to the factl that the armatures are mounted on cantilever springs the styluses have compliance in both lateral and vertical directions. It will also be. seen that due to the tubular construction of. the armatures the ratio of stiffness to mass is relatively high.

In using my improved sound reproducer either one or the other of the styluses. is placed in engagement with the groove of a record. When the stylus is displaced laterally by the modulations of the record groove it moves towards one or the other of the pole pieces causing a flux in the armature which in turn cuts the coil and causes electrical impulses or voltages therein. The coil, in turn, is connected in the usual manner by lead wires 29 and 30 and other lead wires in the reproducer arm to an amplifying and loudspeaking system. Due to the fact that the styluses face in opposite directions they may be used alternately to play the opposite sides of records. Eurthermore, due to the fact that the armatures are arranged in similar relationship to the magnetic'circuitr and tothe same current generator, the two sides of the sound reproducer will operate with a high degree of uniformity with a minimumof distortion and wear on the record and, without the necessity of switching the power from one side of the unit to the other. Modifications may, ofi course, be made in the illustrated and described embodiment without departing from my invention aS set forth in the accompanying claims.

I claim:

l. A phonograph record pick-up of the mag'- netic type comprising: a supporting structure; means including a permanent magnet lixedly carried by said supportingv structure for creating a magnetic iield; a current generator in the form of a single coil xedly carried' by said supporting structure adjacent the magnetic field; and a pair of generally symmetrical moving systems including a pair of armatures in laterally spaced relationship positioned in the magnetic field oi the said coil and in the magnetic eld created by said permanent magnet, springmeans mounted onthe supporting structure and supporting each ofsaid armatures adjacent oneend for vibratory motion inl the magnetic field, said armatures being positioned: in close proximity to the coil so that the induced flux of the armatures cuts the coil upon the vibrationV of the armatures, and' a pair of styluses, said armatures including means supporting the styluses adjacent the free ends. of the armatures so that they project in different directions so that they may be used alternately to engage the sound tracks of records.

2. A phonograph record pick-up of the magnetic type comprising: a supporting structure; means including a permanentY magnet xedly carried by said structure for, creating a magnetic iield; a current generator in the form of a single coil iixedly carried by said supporting structure adjacent the magnetic iield; and a pair of generally symmetrical movingv systems including a pair of armaturesy in laterally spaced relationship positioned in the magnetic eld and projecting through the coil in substantially opposite relationship, a pair of spring means mounted on the supporting structure on respectively opposite sides of the coil and supporting said armatures adjacent respectively opposite ends for` vibra-tory motion` in the magnetic field, said armatures being positioned in close proximity to the coil so that the induced flux of the armatures cuts the coil upon the vibration of the armatures, and a pair ofstyluses, said armatures including means supporting the styluses adjacent the free ends of the armatures on respectively opposite sides ofv the coil for alternate engagementY with the sound tracks of records;

3. A phonograph record pick-up of the magnetic type comprising: a supporting structure; means including a pemianent magnet and pole pieces carried by said structure for creating a magnetic circuit with a pair of spaced gaps therein; a current generator in the form of a single elongated coil having a central opening carried by said supporting structure with the central opening in alignment with the gaps in the magnetic circuit; and a pair of generally symmetrical moving systems including a pair of armatures in laterally spaced relationship positioned in the respective gaps and projecting through the opening in the coil in opposite relationship, a pair of spring means mounted on said supporting structure on respectively opposite sides of the coil and supporting said armatures at respectively opposite ends thereof for vibratory motion in the gaps, said armatures being positioned in close proximity to the coil so that the induced iiux of the armature cuts the coil upon the vibration of the armatures, and a pair of styluses, said armatures including means supporting the styluses adjacent the free ends of the armatures on respectively opposite sides of the coil so that they may be alternately engaged with the sound tracks of records.

' NORMAN C. PICKERING.

REFERENCES CITED The following references are of record in the le of this patent:

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